1. Technical Field
This invention generally relates to semiconductor circuit fabrication, and more specifically relates to antifuses in semiconductor devices.
2. Background Art
The proliferation of electronics in our modem world is in large part due to integrated circuit semiconductor devices. Integrated semiconductor devices are designed and used for widely differing applications. For this reason it is often beneficial to have the ability to xe2x80x9cpersonalizexe2x80x9d a semiconductor device during fabrication. Personalization of a integrated devices involves changing the integrated device to meet specific circuit needs. For example, changing the input and output structure of a device to allow it to be used in multiple applications.
Often, it is not cost effective to create separate fabrication lines, with different masks and such, for each small change in the device for associated circuit requirements. For this reason, specific techniques are used to personalize the device, i.e., to make specific changes in the device to meet a particular need. Some techniques use fuses to customize a device for a particular need. To personalize such a device, some of the available fuses are blown by a laser or other means to make the desired changes to the device and associated circuits. Thus, fuses are blown to make a previously closed connection open. Antifuses are used also used to personalize semiconductor devices. Antifuses are devices that perform the opposite function of a fuse. When a sufficient voltage is applied across an anti-fuse structure the structure becomes permanently shorted, and an electrical connection is made. Thus, antifuses are xe2x80x9copenxe2x80x9d and unconnected until they are xe2x80x9cprogrammedxe2x80x9d to provide a closed connection.
Fuses and antifuses are commonly used to provide redundancy in large scale semiconductor devices such as dynamic random access memory (DRAM) and static random access memory (SRAM) products. In particular, fuses and antifuses are used to access spare bit lines and/or word lines to increase yield potential. Typically, the semiconductor device is built and then tested. Some types of flaws in the device, such as bad bit lines in a DRAM, can be repaired by blowing an appropriate fuse. In the case of fuses, the fuse links can be polysilicon or metal and can be blown by focusing an appropriate pulse of laser energy on the target fuse. When the laser strikes, the fuse link is vaporized and evaporated upward. This makes the previously closed connection xe2x80x9copenxe2x80x9d.
Fuses and antifuses are also used to xe2x80x9cprogramxe2x80x9d devices. For example, a bank of eight fuses can be used as a xe2x80x9cprogramming wordxe2x80x9d, with each fuse being either a one or a zero. Thus programmed, the bank of fuses provides a programming word that is used to control the rest of the device.
There are generally two types of fuses today used in integrated semiconductor devices. The first type is called a xe2x80x9claserxe2x80x9d fuse. These fuses are blown using laser ablation prior to packaging the integrated semiconductor device. The second type of fuse is an xe2x80x9celectronicxe2x80x9d fuse. These fuses are blown by providing an amount of current through the fuse such that the fuseable link breaks down. Electronic fuses have the advantage of being able to be programmed after the device has been packaged.
One difficulty in using fuses and antifuses in integrated circuit devices is their propensity to result in randomly floating voltage levels after programming. For example, a blown fuse is an open circuit and typically has variable resistance. This results in inconsistent amounts of current and voltage across the blow fuse. This inconsistent voltage and current negatively effects digital devices. To overcome this the prior art uses latches that are connected to the fuse or antifuse. The latch produces a solid digital output from the relatively variable fuse or antifuse, with the latched digital output being indicative of the state of the fuse or antifuse. Thus, the variable nature of the fuse or antifuse is dealt with using the latch.
One problem with the use of latches connected to fuses is the amount of area consumed by the latches. Most typical latches used with fuses use up to twelve transistors, resulting in excessive device size. Further, as fuse pitch gets tighter, it becomes more difficult to use these latches with fuses and antifuses.
Therefore, there existed a need to provide an improved structure and method for integrated fuses and antifuses that produces reliable digital outputs while minimizing device size.
According to the present invention, a programable latch device for use in personalizing a semiconductor device is provided that overcomes the limitations of the prior art. The preferred embodiment programmable latch device can use both fuses and antifuses as programmable elements. The programmable latch device provides a solid digital output indicative of the state of the programmable device, and can be reliably read to provide customization and personalization of associated semiconductor devices.
The preferred embodiment programable latch device includes an integrated fuse or antifuse as a programmable element in the latch device. By integrating the programmable element into the latch, device size and complexity is minimized. In particular, the number of transistors required drops considerably when compared to prior art approaches.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.